SkTypes.h: general cleanup

 - SkToBool now inline function.
 - SK_Invalid{Gen|Unique}ID, SK_MSecMax now constexpr.
 - SkNoncopyable deleted methods marked private.
 - Consistant comment style.

Change-Id: I1af6889fdf4274d6d698e8f11b29075dbe39ba12
Reviewed-on: https://skia-review.googlesource.com/135446
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
2 files changed